Method and device for reducing the spacing between the jacket tube of nuclear reactor fuel rods and the charge of fuel received therein

ABSTRACT

Method of reducing the spacing between the jacket tube of nuclear reactor fuel rods and the charge of fuel received therein includes pressing and permanently deforming by means of a ringshaped hydraulic pressure cushion a respective ring-shaped zone of the jacket tube onto a body disposed in the tube and having substantially the cross-sectional dimension of the charge of fuel to be received in the tube, and simultaneously advancing the jacket tube and the body stepwise through the pressure cushion, the length of each advancing step being adjusted to the width of the ring-shaped zone.

United States Patent Scharf et al. Apr. 25, 1972 METHOD AND DEVICE FOR[5 References Cited fiiifiiiiifiiifiifi """EDSWESPATENTS T n 2,423,8627/1947 Vorobik... .72/63 x REACTOR FUEL RODS AND THE 2,894,421 7/1959Appel 72/428 x CHARGE OF FUEL RECEIVED 2,986,051 5/1961' Appel ..72/402THEREIN 3,035,340 5/1962 Appel ..29/544 [72] inventors: Hans Schnri,Numbers; Gerhard Bop t, cGeary i Numberg Eckhard Steinberg Erlangen at aI an of y 3,372,460 3/1968 Burns et al. 29/517 X [73] Assignee: SiemensAktiengeselbchalt, Berlin, Ger- -Primary Examiner-Charlie T. Moon many1.4mm": Examiner-Victor A. D. Palma Attorney-Curt M. Avery, Arthur E.Wilfond, Herbert L. [221 Lerner and Daniel J. Tick [2]] App], No.:777,681

' ,[57] ABSTRACT [30] Foreign Application Priority Data I ;Method ofreducing the spacing between the jacket tube of Enuclear reactor fuelrods and the charge of fuel received Nov. 22, 1967 Germany ..P l6 14756.9 therein includes p g and permanently deforming y means of aring-shaped hydraulic pressure cushion a respec- [52] Cl 47 6 :tivering-shaped zone of the jacket tube onto a body disposed 5 I] Cl 17/00in the tube and having substantially the cross-sectional dimen- 58}Field 72/63 sion of the charge of fuel to be received in the tube, andsimul- "l/ 5 3370 3'67, taneously advancing the jacket tube and the bodystepwise through the pressure cushion, the length of each advancing stepbeing adjusted to the width of the ring-shaped zone.

1 1 Claims, 4 Drawing Figures 1 METHOD AND DEVICE FOR REDUCING THESPACING BETWEEN THE JACKET TUBE OF NUCLEAR REACTOR FUEL RODS AND THECHARGE OF FUEL RECEIVED THEREIN Our invention relates to method anddevice for reducing the spacing between the jacket tube of nuclearreactor fuel rods and the charge of fuel received therein.

Nuclear reactor fuel rods are generally formed of a jacket tube, forexample of stainless steel, containing a charge of nuclear fuel, forexample in the form of cylindrical tablets. Due to the heating of suchnuclear fuel rods during the operation of the reactor, thermal expansionof the involved materials occurs, the thennal coefficient of expansionof the jacket tube material in some cases is greater than that of thenuclear fuel.

If a specific maximum play or spacing of the fuel tablets in the jackettube is exceeded in such reactors, longitudinal folds produced bypressure of the coolant occur at the fuel rod under reactor operatingconditions, leading to a break in the jacket tube as a result ofexpansion fatigue for cyclic stresses due to changes in temperature. Theleast possible play between the jacket tube and the fuel tablet contentsthereof is therefore required when the fuel rods are in the cool statewhich necessarily calls for very narrow tolerances both for the jacketas well as the fuel. The allowable play is dependent upon the material,the state or condition of the material and the dimensions of the jackettube; in a disadvantageous case, the play can approach zero.

Quite independently of the fact that the maintenance of such productiontolerances is extraordinarily difficult (the jacket tubes and fueltablets must be divided into classes of tolerances) and is thereforeaccompanied by correspondingly large expenses, great technicaldifficulties are encountered in the production of the fuel rod,especially during the process of filling it with the fuel. This becomesimmediately clear when it is realized that the play or gap betweenjacket tube and fuel tablets, as the latter are being inserted in thejacket tube, need be at most 30 for example, while the thickness of ahuman hair, in contrast thereto, is ,about 50 to 80p.

To solve this problem, different ways have heretofore been proposed andinvestigated, all of which are based on providing a greater clearancebetween fuel rod jacket tube and fuel tablet. Thus, for example,attempts have been made to uniformly press the jacket tube of thecompleted fuel rod onto the fuel rod core inside a pressure vessel witha pressure medium such as water, for example. Therewith only relativelysmall clearances between the fuel charges and the jacket tube are to beeliminated since the limit for the formation of folds is rapidlyattained. Also the pressing of the jacket tube onto the fuel core withthe aid of shock waves does not lead to any satisfactory results.Although relatively large clearance gaps between the fuel tablets andjacket tube can be diminished by such a method, it is hardly capable ofbeing used for thinwalled steel tubes due to the dislocations of thetablets that are produced. The use of a swaging process is ruled outbecause the fuel tablets (sintered bodies) become destroyed thereby. Infact, heretofore, no satisfactorily operating method for solving theaforementioned problem has become known.

It is accordingly an object of our invention to provide method anddevice for reducing the clearance gap between the jacket tube of nuclearreactor fuel rods and the charge of fuel received therein which can beused for thin-walled steel jacket tubes and which will not damage thefuel tablets contained therein.

With the foregoing and other objects in view, we provide in accordancewith our invention, method for reducing the clearance gap between thejacket tube of nuclear reactor fuel rods and the charge of fuel receivedtherein, which comprises pressing and permanently deforming a respectivering-shaped zone of the jacket tube onto the charge of fuel by means ofa ring-shaped hydraulic pressure cushion as the jacket tube and fuelcharge are fed stepwise through the pressure cushion, the length of thesteps being adjusted to the width of the ringshaped zone. The jackettube is advanced stepwise through the ring-shaped hydraulic pressurecushion which is subjected to pressure at a frequency corresponding tothe stepwise advance, and thereby progressively effects the requiredreduction in the diameter ofthe fuel rod jacket tube. Tests that havebeen carried out have shown that in this way an original diametricspacing or gap of up to about 500p. can be eliminated without theformation of a fold in the jacket tube. The residual spacing or gapbetween fuel and jacket tube determined by the natural resilience of thematerial of the jacket tube is about 20p. and is so small that even forsimulated reactor conditions no fold formation will occur in the jackettube.

To obtain a uniformly smooth surface, it is thereby expedient that thepressure zones overlap one another somewhat whereby a mutual alignmentor adjustment of the fuel tablets occurs and dislocations are notproduced. Contrariwise, it is obviously also possible, by employing agreater length of feed step and therewith a greater spacing of thepressure zones, to obtain a wave-shaped tube surface which offers theexpectation of possibly more advantageous heat transfer characteristicsfor the coolant. The method of our invention is also utilizable forcalibrating thin-walled tubes. In accordance with fuel rod, thecalibrating mandrel is replaced by a column of fuel tablets. Since anincrease in the length of the jacket tube occurs with the method of ourinvention, it is advantageous for the production of fuel rods, to holdtogether the column of tablets by a slight spring pressure from oneside, and thereby to avoid indentations of the jacket tube in the gapsthat may form between the tablets. If it should be desired, however, tohave a specific spacing between the fuel tablets, for example for thepurpose of receiving decomposition gas therein, a spacing of the tabletswith the formation of defined intermediate chambers is effected by theseindentations of the jacket tube in the small spaces between thefissionable fuel tablets.

Other features which are considered as characteristic for the inventionare set forth in the appended claims.

Although the invention is illustrated and described herein as embodiedin method and device for reducing the spacing between the jacket tube ofnuclear reactor fuel rods and the charge of fuel received therein, it isnevertheless not intended to be limited to the details shown, sincevarious modifications and structural changes may be made therein withoutdeparting from the spirit of the invention and within the scope andrange of equivalents of the claims.

The construction and method of operation of the invention, however,together with additional objects and advantages thereof will be bestunderstood from the following description of specific embodiments whenread in connection with the accompanying drawing, in which:

FIGS. 1a and 1b are diagrammatic cross sectional views respectively ofan unstressed'fuel rod and of a fuel rod formed with a longitudinal foldclue to compression;

FIG. 2 is a diagrammatic longitudinal sectional view of the fuel rodshown in FIG. la; and

FIG. 3 is a device for carrying out the method of reducing the gapbetween the jacket tube of a fuel rod and a charge of the fuel rod isseen after it has been subjected to a pressure loading during operationof a nuclear reactor in which it has been disposed or after an attempthas been made to press the jacket tube onto the fissionable fuel core byone of the aforementioned prior art methods. The consequent stressing ofthe jacket tube 10 has thus produced a longitudinal fold 12 thereinwhich, due to the varying stresses imposed on the fuel rod duringoperation of a reactor, tend toward the manifestation of fatigue andthereby result in the production of breaks in the jacket tube.

In the longitudinal sectional view of a partial length of a fuel rodshown in FIG. 2, a portion 11 of the jacket tube 10 has been pressed inaccordance with the method of the invention, over the column offissionable material 61.,The portion 11 originally had the dimensions ofthe tube portion 10 so that the fuel tablets 61 were readily able to bereceived therein without difficulty due to adequate clearance 13 betweenthe tablets 61, on the one hand, and the tube 10 on the other hand. Inview of the permissible and desirable large spacing 13, the division ofthe respective fissionable fuel tablets as well as jacket tubes intotolerance classes can be dispensed with.

In FIG. 3 there is shown diagrammatically a device for carrying out themethod of the invention and, in the illustrated embodiment, especiallyemployed for calibrating jacket tubes by means of a floating calibratingmandrel 6 instead of the column of fuel tablets 61. The jacket tube 10is advanced stepwise with the aid of a suitable transporting device 4through a compression device formed of a disc-shaped pressure-tighthousing 21, containing a ring-shaped pressure chamber 25 in the interiorthereof. The pressure chamber 25 is closed off from the jacket tube 10by a ring-shaped sealing member 3 which serves simultaneously as apressure cushion. The ringshaped chamber 25 is connected to a pressureproducer 5 which presses the pressure cushion 3 against the jacket tubein time or cadence with the stepwise feeding of the transport device 4,and thereby presses the jacket tube at 11 onto the calibrating mandrel6. The pressure producer 5 can be a pump, for example, with appropriatevalves or, as shown in the embodiment of FIG. 3, is an electromagneticpressure producer that is provided with an electromagnet coil 53 and anarmature 52. When the coil 53 is energized, the armature 52 actuates thepressure piston 51 and, after one operating stroke, is returned to itsinitial position by a reset compression spring 54. Due to the uniformforce of the magnet 53, a continually constant operating pressure isattained that is independent of the length of stroke of the piston 51(and therewith independent of the deformed volume. A supply tank 55 forthe pressure medium such as high pressure oil, for example, communicateswith the cylinder in which the pressure piston 51 is reciprocated sothat any possible pressure medium losses are automatically adjusted orcompensated.

the transporting device 4 is made up of a pair of clamping jaws orgrippers 43 which are slidingly mounted in a tensioning lock 42. Thetensioning lock proper is maintained in the position shown in FIG. 3 byreset compression springs 41. The clamping jaws 43 are advanced intransporting direction toward the left-hand side of FIG. 3, for example,with the aid of an eccentric push rod 44, so as to feed the jacket tube10 in that direction. The clamping jaws 43, due to the conical guideformed in the tensioning lock 42 comes into force-locking engagementwith the jacket tube 10 and thereby entrains the latter. In the limitposition of the electrical feed magnet armature 52 of the pressureproducer 5, the magnet coil 53 is energized periodically by a cam switchmechanism 46, 47 connected with the drive 45 for the eccentric push rod44, and the oil in the chamber 25 is accordingly compressed by thepressure piston 51. The pressure cushion 3 then presses the jacket tube10 onto the calibrating mandrel 6 located within the tube 10. Of course,instead of a calibrating mandrel 6, a column of nuclear fuel tablets 61proper, as shown in FIG. 2, can be substituted for the mandrel 6. Bythis compression step, the jacket tube 10 is held in the position shownin FIG. 3, while the eccentric rod 44 then withdraws the clamping jaws43 toward the right-hand side of FIG. 3, so that the jaws 43 open andthe tensioning lock 42 is returned by the reset spring 41 to the initialposition thereof. In the interim, the jacket tube deforming operation iscompleted, the electrical feed magnet 53 is switched off, the resetspring 54 forces the pressure piston 51 back toward the right-hand sideof FIG. 3, and thereby relieves the pressure cushion 3. Thereafter, theeccentric push rod 44 again pushes the clamping jaws 43 together withthe jacket tube 10 the adjusted step distance toward the left-hand sideof FIG. 3, the jacket tube deforming operation is again instituted andthe aforementioned sequence of events takes place once again. The deviceis best adjusted so that the zones of deformation overlap somewhatwhereby an absolutely uniformly smooth surface of the deformed jackettube is obtained.

Obviously the method of the invention can be carried out with deviceshaving a structure that varies from that shown in the embodiment of FIG.3.

It should be noted that in carrying out the method of charging fueltablets into a jacket tube, a considerably shorter amount of time isrequired than had to be expended therefor heretofore by previouslyemployed methods. The pressing of the jacket tube onto the mandrel orfuel tablet column takes about 1 minute per meter. Therewith, allprerequisites are met for including these operating steps also in anormal manufacturing flow.

We claim:

1. Method of reducing the spacing between a jacket tube of larger crosssectional dimension of a nuclear reactor fuel rod and a body such as acharge of fuel of smaller cross sectional dimension receivable in thejacket tube or a mandrel of the same cross sectional dimension as thecharge of fuel receivable in the jacket tube which comprises pressingand permanently deforming by means of a ring-shaped pressure cushion arespective ring-shaped zone of the jacket tube onto the body, andsimultaneously advancing the jacket tube and the body stepwise throughthe pressure cushion, the length of each advancing step being adjustedto the width of the ringshaped zone.

2. Method according to claim 1, wherein the body is a floating mandrel,and the ring-shaped jacket tube zone is pressed and permanently deformedonto the floating mandrel.

3. Method according to claim 1, wherein the body is a charge of fuel,and the ring-shaped jacket tube zone is pressed and permanently deformedonto the charge of fuel received therein.

4. Device for carrying out a method of reducing the spacing between ajacket tube of larger cross sectional dimension of a nuclear reactorfuel rod and a body such as a charge of fuel of smaller cross sectionaldimension receivable therein or a mandrel of the same cross sectionaldimension as the charge of fuel receivable in the jacket tube,comprising a ring-shaped hydraulic pressure cushion and means forstepwise advancing through the pressure cushion a jacket tube with thebody disposed in the tube, said pressure cushion being actuable forpressing and permanently deforming a respective ring-shaped zone of thejacket tube onto said body, said ring-shaped zone having a widthcorresponding to the length of each advancing step of said jacket tube.

5. Device according to claim 4, wherein said pressure cushion consistsof oil-tight, elastic sealing material, and is disposed in a ring-shapedmetallic pressure chamber for sea]- ing said chamber from said jackettube.

6. Device according to claim 4, including means containing asubstantially incompressible medium, said pressure cushion beingconnected to said means so as to be subjected to pressure exerted bysaid medium and means for varying said pressure in cadence with saidstepwise advance for imparting a sequential compression action to thejacket tube.

7. Device according to claim 6 including a high pressure pump, andcontrol valve means connected therewith for pressurizing said medium.

' pressure cushion is a pair of clamping jaws, and an eccentric driveconnected thereto for actuating the same.

10. Method of claim 1 for reducing the spacing between a jacket tubehaving a waveshaped surface and the body receivable therein whichcomprises adjusting the length of the advancing steps of the tube sothat they are longer than the width of the ring-shaped pressure zones.

11. Method of calibrating thin-walled tubes which comprises pressing andpermanently deforming by means of a ringshaped pressure cushion arespective ring-shaped zone of a tube onto a mandrel disposed in thetube and having a predetermined cross-sectional dimension andsimultaneously advancing the tube stepwise through the pressure cushion,the length of each advancing step being adjusted to the width of thering-shaped zone.

* t l i

1. Method of reducing the spacing between a jacket tube of larger crosssectional dimension of a nuclear reactor fuel rod and a bOdy such as acharge of fuel of smaller cross sectional dimension receivable in thejacket tube or a mandrel of the same cross sectional dimension as thecharge of fuel receivable in the jacket tube which comprises pressingand permanently deforming by means of a ring-shaped pressure cushion arespective ring-shaped zone of the jacket tube onto the body, andsimultaneously advancing the jacket tube and the body stepwise throughthe pressure cushion, the length of each advancing step being adjustedto the width of the ring-shaped zone.
 2. Method according to claim 1,wherein the body is a floating mandrel, and the ring-shaped jacket tubezone is pressed and permanently deformed onto the floating mandrel. 3.Method according to claim 1, wherein the body is a charge of fuel, andthe ring-shaped jacket tube zone is pressed and permanently deformedonto the charge of fuel received therein.
 4. Device for carrying out amethod of reducing the spacing between a jacket tube of larger crosssectional dimension of a nuclear reactor fuel rod and a body such as acharge of fuel of smaller cross sectional dimension receivable thereinor a mandrel of the same cross sectional dimension as the charge of fuelreceivable in the jacket tube, comprising a ring-shaped hydraulicpressure cushion and means for stepwise advancing through the pressurecushion a jacket tube with the body disposed in the tube, said pressurecushion being actuable for pressing and permanently deforming arespective ring-shaped zone of the jacket tube onto said body, saidring-shaped zone having a width corresponding to the length of eachadvancing step of said jacket tube.
 5. Device according to claim 4,wherein said pressure cushion consists of oil-tight, elastic sealingmaterial, and is disposed in a ring-shaped metallic pressure chamber forsealing said chamber from said jacket tube.
 6. Device according to claim4, including means containing a substantially incompressible medium,said pressure cushion being connected to said means so as to besubjected to pressure exerted by said medium and means for varying saidpressure in cadence with said stepwise advance for imparting asequential compression action to the jacket tube.
 7. Device according toclaim 6 including a high pressure pump, and control valve meansconnected therewith for pressurizing said medium.
 8. Device according toclaim 6 including an oil-filled cylinder connected to saidmedium-containing means and a magnetically actuable piston, displaceablein said cylinder for periodically pressurizing said pressure medium andsaid pressure cushion.
 9. Device according to claim 4, wherein saidmeans for advancing the jacket tube stepwise through said ring-shapedpressure cushion is a pair of clamping jaws, and an eccentric driveconnected thereto for actuating the same.
 10. Method of claim 1 forreducing the spacing between a jacket tube having a wave-shaped surfaceand the body receivable therein which comprises adjusting the length ofthe advancing steps of the tube so that they are longer than the widthof the ring-shaped pressure zones.
 11. Method of calibrating thin-walledtubes which comprises pressing and permanently deforming by means of aring-shaped pressure cushion a respective ring-shaped zone of a tubeonto a mandrel disposed in the tube and having a predeterminedcross-sectional dimension and simultaneously advancing the tube stepwisethrough the pressure cushion, the length of each advancing step beingadjusted to the width of the ring-shaped zone.